1. Field of the Invention
The present invention relates to a device to reduce distortion in photogrammetry. More specifically, the present invention is drawn to a device that reduces or eliminates distortion in forensic photography.
2. Description of Related Art
Photogrammetry is the art or science of obtaining reliable measurements by means of photography. Some categories of photography may use a reference or object within the photographed field to give context to the object or location photographed. For example, in forensic photography of evidence, a physical reference scale aids in showing the size, dimension, or orientation of the item photographed. This is sometimes referred to as a category of forensic, close in photogrammetry.
Forensic photography is used in both civil and criminal proceedings, where the accuracy of recording relevant information is important. The U.S. Federal Bureau of Investigation (FBI) specifies use of an L-shaped reference scale that has a 30 cm long first arm and a 15 cm long second arm, each having a 15 cm straight scale. The scales are graduated and alternate in black and white for visibility. This “Bureau” reference set is sometimes referred to as the photomacrographic scale set.
Crimes that involve bitemarks show dramatically the difficulty of photographing evidence consistently and accurately, in that a bitemark is a difficult subject to photograph. A bitemark is commonly defined as a physical change in an object caused by its contact with the biter's teeth. In other words, a bitemark is the representative pattern left in a bitten object or tissue, which is caused by the impression of the dental structure of the biting animal or person. A typical human bitemark is an oval patterned injury having two opposing, U-shaped arches, separated at their bases where the upper and lower jaws come together. On the edges of the arches may be additional abrasions, contusions, or lacerations caused by the teeth.
Bitemark characteristics can be used to identify the biter. The characteristics of bitemarks fall into “class” and “individual” characteristics. Class characteristics are common to a group, and can be used to distinguish groups, such as a bitemark of a child from a bitemark of an adult. Individual characteristics differentiate between individuals and may lead to the identity of the specific biter or perpetrator. The number, specificity, and accuracy of reproduction of individual characteristics within a bitemark improve the confidence of bitemark identification.
Odontology is the study of the structure, development, and abnormalities of teeth. When applied to forensics, odontology (or forensic dentistry) includes the legal, evidentiary aspects of investigative dentistry, such as the study of bitemark characteristics with the object of ascertaining the facts surrounding a biting. Thus, odontology is a specialized role in effective crime scene investigation.
An early step in processing the evidence of any crime scene is to photograph the scene using still photography and other visual media. The standards for photographic documentation of a bitemark are provided within the American Board of Forensic Odontology (ABFO) Bitemark Analysis Guidelines. According to the guidelines, photography is preferably performed under an odontologist's direction to ensure accurate and complete documentation of the bite site.
Bitemark analysis guidelines state that an ABFO No. 2 metric scale should be used in order to demonstrate, within the photographs, the size and spatial relationship of bitemark characteristics. The ABFO No. 2 metric scale features both linear and circular graduations in the horizontal and vertical directions. Three crosshair circles aid in compensating for distortion from oblique camera angles. Contrasting measuring bars, 18% gray scale, and the L-shape further enable odontologists to analyze the relative location, size, and orientation of the characteristics of a bitemark from a photograph.
Correct placement of the ABFO No. 2 scale is critical to accurate photographic recordation of bitemark characteristics. The L-shaped scale should be situated on the same plane and adjacent to the bitemark. The critical close-up photographs should be taken in a manner that eliminates distortion that could interfere with a determination of the characteristics of the bitemark.
For example, when the ABFO No. 2 scale and the injury are on the same plane, but the camera angle is not perpendicular to that plane, then the resulting photograph will be subject to angular distortion. Inaccurate positioning of the bite site, the camera, or the ABFO No. 2 scale can create perspective and parallax distortion of the captured image. With such distortion, otherwise similar photographs may show different photogrammetric characteristics.
There are four general types of photographic distortion associated with L-shaped forensic scales. If any photographic distortion exists, it must be corrected before a meaningful comparison analysis can be accomplished. If the image is severely distorted, the distortion may not be correctable and the photograph(s) may not be useable and the subject matter must be re-photographed. Unfortunately, physical evidence is often short-lived, fragile, or transitory in nature and a second photographic opportunity will not be available.
The first type of photographic distortion, Type I angular distortion, occurs when a scale is positioned parallel to the plane of the photographic subject, but the camera is not perpendicular to the plane of the scale and the photographic subject. For example, the scale and bite mark are co-planar, but the plane of the camera back is not parallel to the plane of the scale and bite mark.
The second type of photographic distortion, Type II distortion, occurs when the scale is not in the same plane as the photographic subject (i.e., the bite mark). Thus, the proportions of the photographic subject (i.e., the injury pattern) are not accurately ascertainable.
The third type of photographic distortion, Type III distortion, occurs when one leg of a two-dimensional scale has perspective distortion but the other leg does not. Again, the proportions of the photographic subject (i.e., the injury pattern) are not accurately ascertainable.
The fourth type of photographic distortion, Type IV distortion, occurs when the scale itself is skewed. For example, a portion of the scale is bent, twisted, or curled.
While these are not the only types of potential photographic distortion, these encompass most of the physical distortion seen in evidentiary photographs, such as, for example, bite mark photographs.
The bitemark photographs are recorded within the crime scene photographic log, and become part of the descriptive evidence of the crime scene. The close-up bitemark photographs are important to enable subsequent analysis of the bitemark characteristics by an odontologist.
During analysis of the bitemark photographs, the odontologist will determine a number of facts regarding the bitemark, such as anatomical location, surface and skin characteristics, underlying structure, the shape of the bitemark, (e.g. essentially round, ovoid, crescent, etc.), color, size (i.e., vertical and horizontal dimensions of the bitemark), types of injuries (e.g., petechial hemorrhage, contusions, incisions, etc.), position of maxillary and mandibular arches, location and position of individual teeth, intradental characteristics, etc. The forensic odontologist will then compare the bitemark characteristics from the crime scene with photographs, plaster casts, and/or other evidence from examination of a suspect, which typically includes the results of an intra-oral examination.
Frequently, however, an odontologist is not among the first responders to perform the photographic recordation of a crime scene. Access to the victim after the crime may also be limited for a variety of reasons. Thus, a first responder, who may have minimum photographic training and possibly none in bitemark photography, may be required to photograph the bitemark. Depending on the nature of the incident and sensitivity of the occurrence, the first responder may have limited time to record the bitemark characteristics correctly.
The wide angle orientation photograph may well be within the capability of a first responder trained in general photography. However, the first responder may be unfamiliar with the peculiar requirements for close-up photography of a bitemark. In particular, a first responder is unlikely to have sufficient training in the proper use of the ABFO #2 scale to accurately record the bitemark characteristics. Unfortunately, this can lead to distortion, unreliable photographs, and nonstandard characterization of the bitemark.